Never mind what I said about that WSJ/NBC poll yesterday. This is the strongest evidence yet that Rubio’s coming on in Iowa.

I’d pay cash money to know what Cruz’s internal polling is showing now.

Senator Ted Cruz, scrambling to put down a growing threat in Iowa from Senator Marco Rubio, is shifting nearly all of his negative advertising from Donald J. Trump to Mr. Rubio for the final three days of the caucuses.

Mr. Cruz intends to direct his firepower at his Senate colleague after days of seeing Mr. Rubio inch up both in public polling and his own private surveys, according to two advisers to Mr. Cruz who spoke on the condition of anonymity. After leading in the polls in Iowa for much of the last month, Mr. Cruz has slipped into second behind Mr. Trump in most public surveys.

The change of direction marks an abrupt shift, reflecting how volatile the race in Iowa remains: Mr. Cruz’s campaign only began airing negative spots against Mr. Trump this week and just put their first attack ad up against Mr. Rubio on Thursday on Iowa television.

A diehard Cruz fan assures me on Twitter that this is purely a matter of Cruz running up the score. He’s such a lock to win the caucuses via his ground game, despite trailing Trump routinely now by seven points or more in Iowa polls and notwithstanding a lackluster debate last night, that he’s better off using what little time remains to make sure Rubio finishes as far back as possible before New Hampshire. If true, that’s an … interesting strategy for a guy who’s spent the last 10 days telling Iowans that the race is neck and neck and that if Trump wins Iowa he may be unstoppable. Imagine a Cruz donor being told today “It’s in the bag so we’re going to spend the last 72 hours playing a prevent defense against Rubio” when the number of first-time caucusgoers for Trump on Monday is still a black box.

Even Team Cruz isn’t trying that spin. Their take is that because Cruz’s Super PACs are attacking Trump now, the campaign itself can afford to spend some money to try to hold Rubio back. Okay, but if Iowa’s still competitive, you would think Cruz would throw everything he’s got at Trump in hopes of derailing him before he builds up momentum. If Cruz loses narrowly to Trump and then Trump swamps New Hampshire, Cruz’s task in South Carolina will be much harder than if he went kitchen-sink on Trump now and won Iowa narrowly. It sure looks as if Cruz has quietly become convinced that second place in Iowa is the likeliest outcome for him and he’s desperately trying to hold Rubio to third. Cruz finishing second in the caucuses would be a heavy blow but he can still use it to claim a two-man race next week with Trump. Finishing third behind Rubio might be a campaign-killer since it would show that Cruz can’t even top Rubio in states where the electorate is supposed to favor the “true conservative” with a shelf full of evangelical endorsements.

Here’s another possibility, I guess:

Alternate strategery theory: Cruz camp attacking Rubio precisely to raise expectations for a Rubio "surge".

(Overthinking? Campaigns do.)

— Dan McLaughlin (@baseballcrank) January 29, 2016

Okay, but those are precious dollars to be spending on what would amount to a big media fake-out when they could be going towards tearing down Trump. The odds of Rubio finishing second, by the way, are currently 22 percent per Nate Silver. He’s got a 10 percent chance of shocking the world and winning the caucuses outright, which, implausible though it may seem, would give us a week of “Is Rubio about to run the table?” narratives. If he can’t win, though, it’s obvious who he’s hoping will come out on top:

The Florida senator and his advisers have concluded that a head-to-head battle with Mr. Trump over the next several weeks would be much more advantageous than one with Senator Ted Cruz of Texas, whose success would greatly complicate Mr. Rubio’s hopes of consolidating his support inside the Republican Party.

A victory by Mr. Trump would send panicked Republicans toward Mr. Rubio, his campaign reasons, especially donors who have been reluctant to get behind Mr. Rubio because their allegiances are with other candidates.

A victory by Mr. Cruz, however, would give the Texas senator a lift in states that hold later primaries and caucuses, and would draw voters away from Mr. Rubio. And with internal polling showing significant overlap with Cruz voters, the sooner Mr. Cruz can be hobbled, the better, Rubio advisers say.

You can, I guess, interpret Cruz’s new strategy of attacking Rubio as a response to that, although I don’t see the point of it. Trump is the likely beneficiary of Rubio’s attacks on Cruz; if Cruz wants to counter that, he’s better off attacking Trump than Rubio. Only one thing is clear as Iowa approaches maximum chaos, my friends: Huckabee and Santorum will both do terribly on Monday night, and it’ll be glorious.